Always confused, permanently invisible monsters that only know how to
check your electricity resistance are not very fun to fight. For
vaults, I've replaced many instances of vapours with wind drakes where
the "air" is the theme, replaced a couple instances with lightning
spires where the theme was electricity or with thorn hunters if the
theme is merely swamp. Other instances have been outright removed. For
the cloud mage wizlab, I've replaced vapours with wind drakes but have
down-weighted them relative to air elementals and insubstantial wisps.

For the foxfire card, I've moved vampire mosquitos into the position
where vapours were, put insubstantial wisps as lower-power summons
behind fireflies, since the latter got a buff some time ago, and added
killer bees in between insubstantial wisps and fireflies to keep the
number of summon types the same.